1029 - Variable for substitution '%s' is not a string
(Type: <%s>).

Description
A string substitution was attempted with a non-string variable.
Example
Config:
.MyBool = true .MyString = '$MyBool$'
Output:
c:\Test\fbuild.bff(2):(15) FASTBuild Error #1029 - Variable for substitution 'MyBool' is not a string (Type: <Bool>). .MyString = '$MyBool$' ^ \--here
Fix:
.MyOtherString = 'string' .MyString = '$MyOtherString$'